The present invention concerns a method for calibrating an accelerator pedal during driving operation, in which the mechanical position of the accelerator pedal is converted by at least one potentiometer to an electrical signal value and read in by an electronic engine control unit.
The operating point of an internal combustion engine can be preset by an accelerator pedal. The mechanical position of the accelerator pedal is converted by at least one potentiometer (three potentiometers are usually used) to an electrical signal and read in by an electronic engine control unit. Temperature effects and mechanical misalignment cause a change in the association of the mechanical position of the accelerator pedal to the electrical signal value of the connected potentiometer. Moreover, when several potentiometers are used on an accelerator pedal, the signal values are not identical, for example, in the idle position.
DE 36 12 904 A1 describes a method for calibrating an accelerator pedal during driving operation by means of an adaptive learning program. In a first step, the current signal values of the potentiometers are compared with an idle limit and a full-load limit to determine permissibility. If the signal values are permissible, then, in a second step, the current signal value is compared with the preceding signal value. If, for example, the current idle signal value is less than the preceding idle signal value for this potentiometer, then the current idle signal value is set as the determining value for the idle position of the accelerator pedal. The idle signal value is thus adapted towards smaller values. Similarly, the full-load signal value is adapted towards larger values, and the learned value is set as the determining value for the full-load position of the accelerator pedal. To protect against error, a timing element is provided, by which the signal values are set back to the given idle or full-load limit if, for example, the current idle signal value is at a higher value than the learned idle signal value. In practice, the on-board supply voltage is often superposed by interference voltage pulses (spike, load dump), which, with the described calibration method, which can simulate, for example, a learned idle signal value that is too small. This means that despite an unactuated accelerator pedal, the electronic engine control unit electrically detects an actuated accelerator pedal. An analogous situation applies to the learned full-load signal value. The critical point is thus that the idle and full-load position are temporarily no longer detected by the electronic engine control unit during driving operation, and the signal values in between are interpreted falsely.
To solve the problem of the falsely learned idle signal value, DE 196 28 162 A1 provides that the idle position of the potentiometers of the accelerator pedal is calibrated during a visit to a repair shop or at the end of the vehicle production assembly line. In this calibration, the current idle signal value is checked for permissibility and compared with an initial signal value. If the two signal values differ only slightly, then the initial signal value plus an offset is set as the idle signal value. If a signal drift is detected, then the idle signal value is set to an alternative value. During driving operation, this idle signal value is adapted in the direction of smaller values according to the procedure described in DE 36 12 904 A1. An alternative value is also used here when signal drift is detected. Measures for the full-load position are not provided by this source.